Spraying robot system and spraying method wherein spray conditions are determined by using computer

ABSTRACT

An object of the present invention is to provide a thermal spraying robot system capable of automatically determining spraying conditions according to the shape of a workpiece. Shape data on a workpiece ( 9 ) and material data on a thermal spray material are entered by operating a data input unit ( 1 ). A spray condition database  3  stores a plurality of spray parameters for kinds of thermal spray materials and for qualities of sprayed coatings. A path calculating unit ( 4 ) selects values of spray parameters from the spray condition database ( 3 ), and then calculates a path for a thermal spraying gun ( 14 ) according to a predetermined program on the basis of the shape data on the workpiece and the selected values of the spray parameters. The path calculating unit ( 4 ) decides whether or not a thermal spraying operation can be carried out by moving the thermal spraying gun along a calculated path. If it is decided that the thermal spraying operation is feasible, a thermal spraying apparatus  10  carries out the thermal spraying operation in which the thermal spraying gun is moved along the calculated path.

RELATED APPLICATIONS

This application is a national stage application of PCT/JP97/03796,filed Oct. 21, 1997.

TECHNICAL FIELD

The present invention relates to a thermal spraying method using acomputer for automatically determining spray conditions on the basis ofdata on a thermal spray material and the shape of a workpiece to besubjected to thermal spraying, and a thermal spraying robot system forcarrying out the thermal spraying method.

BACKGROUND ART

It is an imperative problem to keep the inlet temperature of a gasturbine at temperatures not lower than 1300° C. to improve the powergenerating efficiency of a gas-turbine power plant. Efforts have beenmade to enhance the refractory quality of liners and transition piecesfor combustors, vanes and blades, which are exposed to ahigh-temperature gas, to solve such a problem, and it is urgentlynecessary to develop heat-resistant materials, i.e., heat-resistantalloys. The withstandable temperatures of state-of-the-artheat-resistant alloys are 850° C. at the highest. Presently availableheat-resistant alloys are not necessarily satisfactory particularly inrespect of resistance to high-temperature oxidation and high-temperaturecorrosion.

Technique intended to deal with raising the inlet temperature of gasturbines coats the surfaces of parts with a ceramic material having asmall conductivity by thermal spraying. This technique is called thermalbarrier coating (hereinafter abbreviated to “TBC”). TBC has effect onsuppressing substantial rise in the temperature of alloy materials. Theeffect in thermal insulation of TBC is considered to lower thetemperature of member by a temperature in the range of 50 to 100° C.

TBC has been applied to combustors and transition pieces used in gasturbine power plants. However, heat insulating ceramic materials havevalues of physical properties greatly different from those ofheat-resistant alloys, which causes the separation of coating layersfrom base metals. To solve such a problem and to enhance the reliabilityof parts, homogeneous coating films having high adhesion must be formed.

When coating the inner surfaces of liners of combustors or the innertransition pieces by thermal spraying, the shapes of the liners and thetransition pieces place restrictions on thermal spraying and hence it isdifficult to carry out thermal spraying without changing the distancebetween a spraying gun and a workpiece, and the inclination of aspraying gun to the surface of a workpiece and, consequently, it isdifficult to form satisfactory coatings over the surfaces of workpieces.To solve such a problem, trials have been made to control a spraying gunautomatically by a robot. Teaching of a path for a thermal spraying gunfor the shape of each workpiece is necessary to maintain the distancebetween the thermal spraying gun and the workpiece constant and tomaintain the thermal spraying gun perpendicular to the surface of theworkpiece throughout a thermal processing process. Therefore, thedevelopment of programs requires much time, and a new program must bedeveloped for every new workpiece.

Accordingly, it has been desired to develop a thermal spraying robotsystem capable of automatically determining spraying conditions and apath for a thermal spraying gun suitable for the shape of everyworkpiece. However, as mentioned above, when processing the liners andtransition pieces of combustors by thermal spraying, interferencebetween the thermal spraying gun and a workpiece and the ability of athermal spraying gun driving mechanism place many restrictions onthermal spraying to coat the inner surfaces of workpieces; that is, thedistance between the thermal spraying gun and the workpiece and theangle of the thermal spraying gun to the workpiece cannot be kept inoptimum ranges and the thermal spraying gun cannot be moved at aconstant moving velocity. Any thermal spraying robot system capable ofautomatically determining spraying conditions according to the shape ofthe workpiece has not yet been provided because of such restrictions.

The present invention has been made in view of the foregoingcircumstances and it is therefore an object of the present invention toprovide a thermal spraying robot system capable of automaticallydetermining spraying conditions according to the shape of a workpiece.

SUMMARY OF THE INVENTION

With the foregoing object in view, the present invention provides athermal spraying robot system comprising an input unit for enteringshape data on the shape of a workpiece and material data on a thermalspray material, a spray condition database storing values of a pluralityof spray parameters dominating the qualities of sprayed coatings andcorresponding to qualities of sprayed coatings for thermal spraymaterials, a path calculating unit for selecting values of the sprayparameters stored in the spray condition database and calculating a pathfor a thermal spraying gun on the basis of the selected values of thespray parameters and the shape data on the workpiece, and a thermalspraying apparatus including the thermal spraying gun, for carrying outa thermal spraying operation on the basis of the selected values of thespray parameters and a path for the thermal spraying gun calculated bythe path calculating unit.

The plurality of spray parameters include, as principal parameters, atleast spray distance d between the workpiece and the thermal sprayinggun, angle θ between the thermal spraying gun and the workpiece andmoving velocity v of the thermal spraying gun relative to the workpiece.The path calculating unit calculates a path for the thermal spraying gunon the basis of the selected values of the principal parameters.

The values of the plurality of spray parameters stored in the spraycondition database include optimum values specifying optimum sprayconditions, and allowable values specifying allowable spray conditionsfor providing sprayed coatings of allowable qualities inferior toqualities of sprayed coatings formed by thermal spraying under theoptimum spray conditions. The path calculating unit selects the optimumvalues of the spray parameters at the beginning.

The path calculating unit changes the optimum value of at least one ofthe principal parameters for the allowable value when it is impossibleto calculate a path for the thermal spraying gun on the basis of theoptimum values of the principal parameters, and recalculates a path forthe thermal spraying gun.

The path calculating unit changes the optimum values of the principalparameters excluding at least one of the principal parameters for theallowable values when it is impossible to calculate a path for thethermal spraying gun on the basis of the optimum values of the principalparameters, and recalculates a path for the thermal spraying gun.

The input unit further has a function to specify the principal parameterhaving the optimum value to be kept unchanged.

If it is impossible to calculate a path for the thermal spraying guneven if the optimum values of all the principal parameters are changedfor the allowable values of the same, the path calculating unit usesvalues of the principal parameters other than the allowable values andrecalculates a path for the thermal spraying gun by using the values ofthe principal parameters other than the allowable values.

The thermal spraying robot system further comprises a display means fordisplaying, when the optimum value of at least one of the plurality ofprincipal parameters is changed for the allowable value, the principalparameter which has been adjusted, in which the input unit further has afunction to determine whether or not thermal spraying is to be executedby using the changed principal parameter.

The present invention provides a thermal spraying method using a thermalspraying apparatus provided with a thermal spraying gun, and a computerfor determining spray conditions, comprising: a data entering step ofentering shape data on the shape of a workpiece and material data on athermal spray material, selecting values of spray parameterscorresponding to the entered material data on the thermal spray materialfrom a spray condition database storing values of a plurality of sprayparameters dominating qualities of sprayed coatings and corresponding toqualities of sprayed coatings for thermal spray materials, a pathcalculating step of calculating a path for the thermal spraying gun onthe basis of the selected values of the spray parameters and the shapedata on the workpiece according to a predetermined program, a decisionstep of deciding whether or not thermal spraying can be carried out bymoving the thermal spraying gun along the calculating path, and athermal spraying step of carrying out a thermal spraying operation onthe basis of the selected values of the spray parameters and thecalculated path for the thermal spraying gun.

The plurality of spray parameters include, as principal parameters, atleast spray distance d between the workpiece and the thermal sprayinggun, angle θ between the thermal spraying gun and the workpiece andmoving velocity v of the thermal spraying gun relative to the workpiece.

The values of the plurality of spray parameters stored in the spraycondition database include optimum values specifying optimum sprayconditions, and allowable values specifying allowable spray conditionsfor providing sprayed coatings of allowable qualities inferior to thequalities of sprayed coatings formed by thermal spraying under theoptimum spray conditions. The optimum values of the spray parameters areselected at the beginning in the selecting step.

If it is decided in the decision step that it is impossible to carry outthermal spraying, the selecting step and the path calculating step areexecuted at least one cycle, and at least one of the values of the sprayparameters selected in the second and the following cycles of theselecting step is an allowable value selected instead of the optimumvalue.

The present invention provides a product produced by coating a workpiecewith a sprayed coating formed by a thermal spraying method using athermal spraying apparatus having a thermal spraying gun and a computerfor determining spray conditions, and comprising a data entering step ofentering shape data on the shape of a workpiece and material data on athermal spray-material, a selecting step of selecting values of sprayparameters corresponding to the entered material data on the thermalspray material from a spray condition database storing values of aplurality of spray parameters dominating qualities of sprayed coatingsand corresponding to qualities of sprayed coatings for thermal spraymaterials, a path calculating step of calculating a path for the thermalspraying gun on the basis of the selected values of the spray parametersand the shape data on the shape of the workpiece according to apredetermined program, a decision step of deciding whether or notthermal spraying can be carried out by moving the thermal spraying gunalong the calculating path, and a thermal spraying step of carrying outa thermal spraying operation on the basis of the selected values of thespray parameters and the calculated path for the thermal spraying gun.

The workpiece is a combustor liner for a combustor or a transition pieceincluded in a gas turbine power plant.

According to the present invention, spray conditions can selectively bedetermined for all kinds of shapes of workpieces without distinctionbetween two-dimensional shapes and three-dimensional shapes, a path forthe thermal spraying gun can be calculated and a thermal sprayingoperation can be carried out. The time necessary for the development ofa thermal spraying program can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a thermal spraying robot system in apreferred embodiment according to the present invention;

FIG. 2 is a flow chart of an operation to be carried out by the thermalspraying robot system;

FIG. 3 is graph showing the relation between the distance between athermal spraying gun and a workpiece, and the level of quality of asprayed coating;

FIG. 4 is a graph showing the relation between the angle between athermal spraying gun and a workpiece, and the level of quality of asprayed coating;

FIG. 5 is a graph showing the relation between the moving velocity of athermal spraying gun relative to a workpiece, and the level of qualityof a sprayed coating;

FIGS. 6(a), 6(b) and 6(c) are typical views of assistance in explainingthe levels of quality of sprayed coatings;

FIGS. 7(a) and 7(b) are a plan view and a side elevation, respectively,of a liner for a combustor, i.e., a workpiece, in Example 1;

FIGS. 8(a) and 8(b) are a perspective view and a partly cutaway sideelevation, respectively, of a transition piece, i.e., a workpiece, inExample 2;

FIG. 9 is a perspective view of a workpiece having the shape of atriangular prism in Example 3; and

FIG. 10 is a perspective view of a frustum-shaped workpiece in Example4.

BEST MODE FOR CARRYING OUT THE INVENTION

A referred embodiment of the present invention will be described withreference to FIGS. 1 to 10.

The construction of a thermal spraying robot system will be describedwith reference to FIG. 1. Referring to FIG. 1, the thermal sprayingrobot system comprises an input unit 1 for entering shape data on theshape of a workpiece 9 to be subjected to thermal spraying and materialdata on a thermal spray material, a spray condition database 3 storing aplurality of spray parameters for kinds of thermal spray materials, athermal spraying apparatus 10 for processing the workpiece 9 by thermalspraying, and a path calculating unit 4 for calculating a path for athermal spraying gun 14 included in the thermal spraying apparatus 10.The spray condition database 3 and the path calculating unit 4constitute a spray condition determining unit 5.

The thermal spraying apparatus 10 comprises the thermal spraying gun 14for spraying the workpiece 9 with droplets of a thermal spray material,and an arm unit 15 holding the thermal spraying gun 14 to move the same.The arm unit is driven by a servomotor, not shown. The thermal sprayingapparatus 10 has a robot driving unit 13 including a driver for drivingthe servomotor. The thermal spraying gun 14 is controlled by the robotdriving unit 13 for movement in vertical and horizontal directions andturning motions.

The thermal spraying apparatus 10 has a thermal spraying control unit 12for controlling parameters indicating the operating condition of thethermal spraying gun 14, i.e., parameters other than principalparameters, which will be described later, such as current, voltage, gasflow and such.

The robot driving unit 13 and the thermal spraying control unit 12 areconnected to a robot control unit 11 which in turn is connected througha data transfer unit 6 to the spray condition determining unit 5. Therobot control unit 11 controls the thermal spraying gun 14 on the basisof spray condition data determined by the spray condition determiningunit 5.

The thermal spraying apparatus 10 is a robot provided with a feedbackcontrol system to which spray condition data (a path for the thermalspraying gun and spray parameters) is transferred as desired values fromthe spray condition determining unit 5.

A display 2, such as a CRT, is connected to the spray conditiondetermining unit 5 and the input unit 1 to display information providedby the spray condition determining unit 5 and input data entered byoperating the input unit 1.

The spray condition database 3 will be described hereinafter. The spraycondition database 3 includes Tables 1 and 2 for thermal spraymaterials. Tabled 1 and 2 contain values of a plurality of sprayparameters specifying spray conditions and determining thermal sprayquality for ZrO₂−8% wt.Y₂O₃, and W and Mo, respectively. The values ofthe spray parameters include “optimum values” specifying optimum sprayconditions A for forming optimum sprayed coatings, and “allowablevalues” specifying allowable spray conditions for forming sprayedcoatings of allowable qualities inferior to those of optimum sprayedcoatings. The allowable spray conditions are classified into primaryconditions B for forming sprayed coatings of qualities comparable tothose of sprayed coatings formed by thermal spraying conforming to theoptimum spray conditions A, and secondary conditions C for formingsprayed coatings of qualities inferior to those of sprayed coatingsformed by thermal spraying conforming to the primary conditions B.

TABLE 1 Spray Condition Database (For ZrO₂-8% wt. Y₂O₃) Optimum PrimarySecondary Spray Parameters conditions (A) conditions (B) conditions (C)Spray distance (mm)  95-100  80-120  60-150 Moving velocity 190-210150-300 100-400 (mm/s) Spraying angle (deg)  80-100  60-120  45-135Current (A) 580-620 520-700 400-800 Voltage (V) 58-62 55-70 50-80 Plasmagas: Ar (l/min) 38-42 35-50 30-70 Auxiliary gas: 6.5-7.5 5-9  3-14 H₂(l/min)

TABLE 2 Spray Condition Database (For W and Mo) Optimum PrimarySecondary Spray Parameters conditions (A) conditions (B) conditions (C)Spray distance (mm)  95-100  80-110  60-130 Moving velocity 190-210150-300 100-400 (mm/s) Spraying angle (deg) 80-95  75-105  55-125Current (A) 580-620 520-700 400-800 Voltage (V) 58-62 55-70 50-80 Plasmagas: Ar (l/min) 48-52 40-60 30-70 Auxiliary gas: 18-22 15-25 10-30 H₂(l/min)

FIGS. 6(a) to 6(c) are typical sectional views of sprayed coatingsformed under different spray conditions, in which indicated at 21 areworkpieces, at 22 are sprayed coatings and at 23 are voids.

As shown in FIG. 6(a), a sprayed coating formed by a thermal sprayingprocess meeting the optimum spray conditions A is relatively dense andhas voids uniformly dispersed therein and its quality corresponds to aquality level A shown in FIGS. 3 to 5. As shown in FIG. 6(b), a sprayedcoating formed by a thermal spraying process meeting the primaryconditions B has more voids than the sprayed coating formed by thethermal spraying process meeting the optimum spray conditions A and itsquality corresponding to a quality level B shown in FIGS. 3 to 5 issomewhat inferior to that of the sprayed coating formed by the thermalspraying process meeting the optimum spray conditions A. As shown inFIG. 6(c), a sprayed coating formed by a thermal spraying processmeeting the secondary conditions C has a quality corresponding to aquality level C shown in FIGS. 3 to 5 inferior to that of the sprayedcoating formed by the thermal spraying process meeting the primaryconditions B. The sprayed coating shown in FIG. 6(c) has excessivelymany large voids and is thin because the yield of the thermal sprayingprocess is low.

As shown in Tables 1 and 2, the spray parameters include distance dbetween the workpiece 9 and the thermal spraying gun 14 (hereinafterreferred to as “spraying distance d”), velocity v of movement of thethermal spraying gun 14 relative to the workpiece 9 (hereinafterreferred to as “moving velocity v”), angle θ of the spraying directionof the thermal spraying gun 14 to the surface of the workpiece 9(hereinafter referred to as “spraying angle θ”). Spraying distance d,moving velocity v and spraying angle θ are called “principal parameters.The spray parameters include, in addition to the principal parameters,voltage applied across the positive and the negative pole of the thermalspraying gun 14 to form an electric arc (hereinafter referred to as“discharge voltage”), current supplied to the thermal spraying gun 14 toform an electric arc (hereinafter referred to as “discharge current”),flow rate of a gas for producing a plasma (argon gas) (hereinafterreferred to as “plasma gas flow rate”) and flow rate of an auxiliary gas(Hydrogen gas) (hereinafter referred to as “auxiliary gas flow rate”).

Practically, the spray condition determining unit 5 among the foregoingcomponents is a computer. Therefore, the path calculating unit 4 isrealized in a program module that is executed by the computer. A programincluding such a program module is stored in a computer readablerecording medium, i.e., an internal storage device, such as a memory ora hard disk included in the computer, or an external storage device,such as a flexible disk or a CD-ROM. The CPU (central processing unit)included in the computer reads and executes steps of the programsequentially to realize the following functions. When the pathcalculating unit 4 carries out calculation and determining steps, theinternal storage device, typically, a memory included in the computer,is used for temporarily storing input data on the workpiece, inputmaterial data on the thermal spray material and calculated data.

The spray condition database 3 to be read by the path calculatingprogram is stored in an internal storage device, such as a hard disk, oran external storage device, such as a flexible disk or a CD-ROM.

Typically, the input unit 1 includes an input device, such as a keyboardor a mouse. The input unit 1 may further be provided with a read devicefor reading the shape data on the shape of the workpiece (CAD data) froma recording medium, such as a flexible disk, a CD-ROM, a MO disk or aDVD, or a data receiving unit capable of directly receiving CAD datafrom a designing computer.

The display 2 is a CRT or a liquid crystal display.

The data transfer unit 6 for transferring data from the spray conditiondetermining unit 5 to the thermal spraying apparatus 10 includes anoutput unit included in the computer, and a cable interconnecting theoutput unit and the robot control unit.

The data transfer unit 6 is not limited to an on-line transfer means andmay be an off-line transfer means using a recording medium, such as aflexible disk, a CD-ROM, a MO disk or a DVD. If the transfer unit 6 isan off-line transfer means, the computer and the thermal sprayingapparatus are provided with a recording device for recording data to therecording medium and a reproducing device for reading data from therecording medium.

The operation of the embodiment thus constructed will be described inconnection with a flow chart shown in FIG. 2.

Material data, i.e., data indicating the kind of a thermal spraymaterial is entered by operating the input unit 1 (step 101). Shape dataon the shape of the workpiece is entered (step 102). Those data may beentered by operating a keyboard or by using an off-line input device,such as a floppy disk or an optical disk. These input data are stored inthe internal storage device of the computer.

Subsequently, the path calculating unit 4 of the spray conditiondetermining unit 5 fetches values conforming to the optimum sprayconditions A (optimum values) for the spray parameters from the spraycondition database 3 (step 103); that is, the path calculating unit 4selects a table corresponding to the material data entered by operatingthe input unit 1 from each table. For example, when Zro₂−8% wt.Y₂O₃ isused, a table included in Table 1 is selected. The path calculating unit4 selects values conforming to the optimum spray conditions A (optimumvalues) from the selected table.

Then, the path calculating unit 4 calculates a path for the thermalspraying gun 14 on the basis of the optimum values of the principalparameters, namely, spraying distance d, moving velocity v and sprayingangle θ, among the spray parameters (step 104). The term “path” usedherein signifies not only position information on the position of thethermal spraying gun 14 but also velocity information on the velocity ofthe thermal spraying gun 14.

The shape of a path to be calculated is determined according to theshape of the workpiece by a path calculating program to be executed bythe path calculating unit 4. For example, when continuously spraying athermal spray material on the inner surface of a workpiece having theshape of a cylinder, a circular cone or a prism, a helical path iscalculated. The path calculating unit 4 calculates a path for thethermal spraying gun 14 on the basis of the shape of the determined pathand the shape of the surface to be coated by thermal spraying so thatthe optimum values of spraying distance d, moving velocity v andspraying angle θ can be used.

As shown in Tables 1 and 2, optimum values can be selected from those inpredetermined ranges. Values of the spraying distance d, moving velocityv and spraying angle θ selected from those in those ranges are used incombination for the calculation of a path for the thermal spraying gun14. A path for the thermal spraying gun 14 is calculated in a similarmanner when the values of some of the principal parameters are selectedfrom those of the primary or the secondary conditions. Although it ispreferable to calculate a path for the thermal spraying gun 14 by usingfixed optimum values of the principal parameters, namely, sprayingdistance d, moving velocity v and spraying angle θ, values of theprincipal parameters need not necessarily be fixed and may be varied inthe predetermined ranges of optimum values.

After the operations in step 104 have been completed, the pathcalculating unit 4 compares the calculated path for the thermal sprayinggun 14 calculated in step 104, the shape of the thermal spraying gun 14of the thermal spraying apparatus 10, the shape of the arm unit 15 andthe shape of the workpiece 9 to decide whether or not the thermalspraying operation can actually be carried out by moving the thermalspraying gun 14 along the calculated path (step 105).

Typically, data on the respective shapes of the thermal spraying gun 14of the thermal spraying apparatus 10, and the arm unit 15 is stored aspart of a program realizing the path calculating unit 4 in the internalstorage device of the computer. If the shape of the workpiece 9 isparticularly complicated, a decision is made in step 105 to see whetheror not the driving ability of the arm unit 15 is high enough to move thethermal spraying gun 14 along the calculated path. A method and anexample of making such a decision will be explained in connection withthe description of preferred embodiments.

If it is decided in step 105 that a thermal spraying operation can becarried out under the optimum spray conditions, the spray conditiondetermining unit 5 transfers data on the spray parameters correspondingto the optimum spray conditions and the path for the thermal sprayinggun 14 calculated in step 104 through the data transfer unit 6 to therobot control unit 11 of the thermal spraying apparatus 10. The data maybe transferred not only by using a communication cable but may betransferred in an off-line mode using a floppy disk or an optical disk.The robot control unit 11 gives data on the path for the thermalspraying gun 14 to the robot driving unit 13 and sends values of thespray parameters other than the principal parameters to the thermalspraying control unit 12. The thermal spraying apparatus 10 moves thethermal spraying gun 14 along the path and carries out a thermalspraying operation according to the values of the spray parameters giventhereto (step 106).

If it is decided in step 105 that a thermal spraying operation can notbe carried out under the optimum spray conditions, the spray conditiondetermining unit 5 makes the display 2 display information to thateffect and makes a query to see which one of the principal parameters(spraying distance d, moving velocity v or spraying angle θ) is the mostimportant parameter (hereinafter referred to as “key parameter”) (step107).

Then, the operator operates the input unit 1 to enter information aboutone or two selected key parameters (step 108).

Then, the path calculating unit 4 keeps the specified key parameter atthe optimum value corresponding to the optimum spray conditions A, andselects values of the principal parameters other than the key parametercorresponding to the primary conditions B, i.e., allowable values, fromthe spray condition database 3 (step 109).

Subsequently, the path calculating unit 4 decides whether or not athermal spraying operation can be achieved by moving the thermalspraying gun along a recalculated path calculated on the basis of theshape and ability of the thermal spraying apparatus 10, the shape of theworkpiece 9 and such (step 110).

If it is decided that a thermal spraying operation specified by thenewly selected values of the spray parameters is feasible, the pathcalculating unit 4 sends the newly selected values of the sprayparameters and the calculated path for the thermal spraying gun 14 tothe robot control unit 11 of the thermal spraying apparatus 10. Thethermal spraying apparatus 10 carries out a thermal spraying operationaccording to the values of the spray parameters by moving the thermalspraying gun 14 along the path to coat the workpiece 9 with a sprayedcoating (step 111).

If it is decided in step 110 that the thermal spraying operation isinfeasible, the path calculating unit 4 of the spray conditiondetermining unit 5 makes the display 2 display information to thateffect (step 112), selects values of the principal parameters other thanthe key parameter corresponding to the secondary conditions, from thespray condition database 3 (step 113).

Subsequently, the path calculating unit 4 decides whether or not athermal spraying operation can be achieved by moving the thermalspraying gun along a recalculated path calculated on the basis of theshape and ability of the thermal spraying apparatus 10, the shape of theworkpiece 9 and such (step 114).

If it is decided that a thermal spraying operation specified by thenewly selected values of the spray parameters is feasible, the pathcalculating unit 4 sends the newly selected values of the sprayparameters and the calculated path for the thermal spraying gun 14 tothe robot control unit 11 of the thermal spraying apparatus 10. Thethermal spraying apparatus 10 carries out a thermal spraying operationaccording to the values of the spray parameters by moving the thermalspraying gun 14 along the path to coat the workpiece 1 with a sprayedcoating (step 115).

If it is decided that the thermal spraying operation is infeasible, thepath calculating unit 4 of the spray condition determining unit 5 makesthe display 2 display information to that effect (step 116), and makes aquery to see if the operator has an intention to change the values ofthe key parameter (step 117).

If the operator decides that the value of the key parameter be changed,steps 108 to 116 are repeated to change the optimum value of the keyparameter, and, if a thermal spraying operation under thus determinedspray conditions is feasible, the spray condition determining unit 5sends the readjusted values of the spray parameters and a calculatedpath for the thermal spraying gun 14 through the data transfer unit 6 tothe robot control unit 11 of the thermal spraying apparatus 10. Thethermal spraying apparatus 10 carries out a thermal spraying operationaccording to the values of the spray parameters given thereto by movingthe thermal spraying gun 14 along the path to coat the workpiece 9 witha sprayed coating.

If it is decided that a thermal spraying operation defined by sprayconditions determined by changing the value of the key parameter andexecuting steps 108 to 116 is infeasible (step 114), the pathcalculating unit 4 selects values of all the principal parameters fromthose of the primary or the secondary conditions, and recalculates apath for the thermal spraying gun 14 (step 118). Step 118 is executedalso when it is decided in step 117 that the value of the key parameterbe not changed.

Subsequently, the path calculating unit 4 decides whether or not athermal spraying operation is feasible under spray conditions calculatedin step 118 (step 119). If it is decided that the thermal sprayingoperation is feasible, the spray condition determining unit 5 sends thereadjusted values of the spray parameters and a calculated path for thethermal spraying gun 14 through the data transfer unit 6 to the robotcontrol unit 11 of the thermal spraying apparatus 10. The thermalspraying apparatus 10 carries out a thermal spraying operation accordingto the values of the spray parameters given thereto by moving thethermal spraying gun 14 along the path to coat the workpiece 9 with asprayed coating (step 120).

If it is decided in step 119 that the thermal spraying operation isinfeasible, the path calculating unit 4 displays information to thateffect and recalculates a possible path for the thermal spraying gun 14(step 121). In step 121 the calculation of a path is carried out even ifthe values of the principal parameters (spraying distance d, movingvelocity v and spraying angle θ) are other than those for the secondaryconditions.

The values of the principal parameters used in the calculation of thepath are displayed by the display 2 and a query is made to the operatorto prompt the operator to decide whether or not the thermal sprayingoperation be carried out according to the values of the principalparameters (step 122).

If the operator decides that the thermal spraying operation according tothose values of the spray parameters may be carried out (step 123), theoperator operates the input unit 1 to enter an instruction to thateffect. Then the spray condition determining unit 5 sends the values ofthe spray parameters to the robot control unit 11, and the thermalspraying operation is carried out by moving the thermal spraying gunalong the calculated path according to the values of the sprayparameters (step 124).

If the operator decides that the thermal spraying operation according tothe thus selected values of the spray parameters is unacceptable, thethermal spraying operation is not executed (step 125).

The following changes may be made in the foregoing flow chart. Thisembodiment executes the thermal spraying operation immediately when itis decided in step 110, 114 or 119 that the thermal spraying operationis feasible (steps 111, 115, 120). A step for making the operator decidewhether or not the thermal spraying operation is executed may beinterposed between steps 110 and 111, between steps 114 and 115 and/orbetween steps 119 and 120.

Although this embodiment coats the entire surface of the workpiece 9 bythermal spraying under the substantially fixed spray conditions, thesurface of the workpiece 9 may be divided into a plurality of regions,and different spray conditions may be determined for different regionsby using different values of the principal parameters, such as theoptimum values for a first region and values of the secondary conditionsfor a second region, which will be explained in connection with thedescription of second to fourth embodiments.

As is apparent from the foregoing description, the foregoing embodimentis capable of automatically determining spray conditions according tothe shape of a workpiece and of significantly reducing time necessaryfor the development of a thermal spraying program.

EXAMPLES

Concrete examples of spray condition determining processes will bedescribed hereinafter. The following description will be made on anassumption that a thermal spray material is ZrO₂−8% wt.Y₂O₃. Stepnumbers used in the following description correspond to the numbers ofthe steps of the flow chart shown in FIG. 2, respectively.

Example 1

Example 1 will be described with reference to FIG. 7. Shown in FIG. 7 isa combustor liner 31, i.e., a workpiece, for a gas turbine power plant.The combustor liner 31 has a generally cylindrical shape. The combustorliner 31 is provided at one end thereof with an opening 31 a of adiameter smaller than the inside diameter thereof and at the other endthereof with an opening 31 b of a diameter equal to the inside diameterthereof. The inside diameter of the combustor liner 31 is dependent onthe power generating ability of the gas turbine power plant; the insidediameter is great for a large output or is small for a small output.

When coating the inner surface of the combustor liner 31 with a heatshield, the inner surface is subjected to a blasting process, the innersurface is coated with a metal layer, and a ceramic layer is formed overthe metal layer. When coating the inner surface, the thermal sprayinggun 14 is inserted through the opening 31 b into a central region of theinterior of the combustor liner 31, and the thermal spraying gun 14 orthe combustor liner 31 is turned to coat the inner surface of thecombustor liner 31.

When coating the inner surface of the combustor liner 31 by thermalspraying, a spray condition determining process was carried outaccording to the flow chart shown in FIG. 2.

Since the combustor liner 31, i.e., the workpiece, has a shaperotationally symmetric with respect to a predetermined axis, the pathcalculating unit 4 calculated a path for the thermal spraying gun 14 instep 104 to move the thermal spraying gun 14 helically with respect tothe inner surface of the combustor liner 31.

Consequently, it was decided in step 105 that the thermal sprayingoperation cannot be carried out with the spraying distance d fixed atthe optimum value, because the inside diameter of the combustor liner 31for a gas turbine of an output capacity on the order of 15,000 kW is onthe order of 200 mm and the thermal spraying gun 14 cannot be held atthe optimum value of spraying distance d in the range of 95 to 100 mm inthe combustor liner 31 owing to its actual dimensions and the shape ofthe arm unit 15.

In this case, the operator selected moving velocity v and spraying angleθ as key parameters by operating the input unit 1 (step 108). Then, apath for the thermal spraying gun 14 was recalculated automatically(step 109) and it was ascertained that a thermal spraying operationunder conditions shown in Table 3, in which optimum values of movingvelocity v and spraying angle θ can be used when the spraying distance dis 80 mm included in the primary conditions (step 110).

The combustor liner 31, i.e., the workpiece, has a shape rotationallysymmetric with respect to a predetermined axis and the shape is fixedwith respect to a direction along the axis. Therefore, the entire innersurface of the combustor liner 31 could be coated with a sprayed coatingformed under the same spray conditions.

TABLE 3 Spray Condition For Combustor Liner Spray Parameters ValuesSpray distance (mm) 80 Moving velocity (mm/s) 200 Spraying angle (deg)90 Current (A) 600 Voltage (V) 60 Plasma gas: Ar (l/min) 40 Auxiliarygas: H₂ (l/min) 7

Example 2

Example 2 will be described with reference to FIG. 8. Shown in FIG. 8 isa transition piece 32 serving as a component part of a gas turbine powerplant. The transition piece 32 has opposite open ends 32 a and 32 b (aninlet and an outlet). As shown in FIG. 8(b), the transition piece 32 hasa curved inner surface of varying curvature and different parts of thetransition piece 32 have different cross sections.

The spray condition determining process including steps 101 to 105 ofthe flow chart shown in FIG. 2 was executed to coat the inner surface ofthe transition piece 32 with a sprayed coating. It was decided that asprayed coating cannot be formed over a middle region of the innersurface of the transition piece 32 by a thermal spraying operation usingoptimum values of spraying distance d, moving velocity v and sprayingangle θ.

The principal reason the thermal spraying operation cannot be carriedout for the middle region of the inner surface of the transition piece32 was that the arm unit 15 holding the thermal spraying gun 14 collidesagainst the brim of the open end of the transition piece 32 when thethermal spraying gun 14 is inserted through either the open end 32 a orthe open end 32 b into the transition piece 32. It was possible to carryout the thermal spraying operation using the optimum values of sprayingdistance d, moving velocity v and spraying angle θ for regions of theinner surface near the open ends 32 a and 32 b.

The spray conditions were kept unchanged for the regions of the innersurface near the open ends 32 a and 32 b, and step 107 and the followingsteps were executed to determine spray conditions for the middle regionof the inner surface of the transition piece 32.

Allowable values (the secondary conditions) of the three key parameterswere selected and a path along which the thermal spraying gun 14 is tobe moved to coat the middle region of the inner surface of thetransition piece 32 was recalculated (step 118), paths for the thermalspraying gun which enable thermal spraying operations under sprayconditions shown in Table 4 could be calculated.

Different values of the parameters were used for coating the regions ofthe inner surface near the inlet and the outlet (open-ends 32 a and 32b) of the transition piece 32 shown in FIG. 8(b), and the middle regionof the inner surface, respectively (step 119).

TABLE 4 Spray Condition For Transition Piece Values For Inlet Values forSpray Parameters and Outlet Region Middle Region Spray distance (mm) 10060 Moving velocity (mm/s) 200 350 Spraying angle (deg) 90 70 Current (A)600 600 Voltage (V) 60 60 Plasma gas: Ar (l/min) 40 40 Auxiliary gas: H₂(l/min) 7 7

Example 3

Example 3 will be described with reference to FIG. 9. Shown in FIG. 3 isa workpiece 34 resembling a triangular prism having opposite open ends.When coating the inner surface of the workpiece 34 resembling atriangular prism with a sprayed coating, the spraying angle θ of thethermal spraying gun 14 cannot be kept at an optimum angle of 90° andthe values of spraying angle θ needs to be varied during a thermalspraying operation. Feasible spray conditions shown in Table 5 weredetermined by calculating a path for the thermal spraying gun 14 byspecifying spraying distance between the thermal spraying gun 14 and theworkpiece as a key parameter.

Different spray conditions were determined for coating end regions ofthe inner surface and for coating a middle region of the same,respectively. The spray conditions for the end regions include anoptimum value for spraying distance d, an allowable value included inthe secondary conditions for moving velocity v, and a value included inthe primary conditions for spraying angle θ. Thus, the sprayingconditions were determined by steps 101 to 114 of the operationexpressed by the flow chart shown in FIG. 2.

The spray conditions for the middle region include a value included inthe secondary conditions for spraying distance d, a value included inthe secondary conditions for moving velocity v, and a value outside therange of values included in the secondary conditions for spraying angleθ. Thus, the spraying conditions were determined by steps 101 to 123 ofthe operation expressed by the flow chart shown in FIG. 2.

TABLE 5 Spray Condition For Triangular Prism Values For Inlet Values forSpray Parameters and Outlet Region Middle Region Spray distance (mm) 10070 Moving velocity (mm/s) 200-350 100 Spraying angle (deg) 60-90 40Current (A) 600 800 Voltage (V)  60 80 Plasma gas: Ar (l/min)  40 40Auxiliary gas: H₂ (l/min)  7 7

Example 4

Example 4 will be described with reference to FIG. 10. Shown in FIG. 10is a frustum-shaped workpiece 35. Numerical values indicated along withlines on FIG. 10 describe inside measurements of the frustum-shapedworkpiece 35.

Since the frustum-shaped workpiece 35 is rotationally symmetric withrespect to a predetermined axis, the path calculating unit 4 calculateda helical path for the thermal spraying gun 14 in step 104 so that thethermal spraying gun 14 is moved helically relative to the inner surfaceof the frustum-shaped workpiece 35.

The calculation showed that the a thermal spraying operation can becarried out for a region near a bottom surface 35 a under sprayconditions using an optimum value of spraying angle θ, and valuesincluded in the primary conditions of spraying distance d and movingvelocity v (step 110).

However, the thermal spraying gun 14 could not be spaced the selectedvalue of spraying distance apart from the a region of the inner surfacenear the smaller end 35 b. Therefore, the system decided that the athermal spraying operation cannot be carried out even if a path for thethermal spraying gun 14 is recalculated by using values of sprayingdistance d, moving velocity v and spraying angle θ included in thesecondary conditions (step 119 in the flow chart shown in FIG. 2).

The display 2 displayed information telling that a thermal sprayingoperation can be achieved if the spraying distance between the thermalspraying gun and the workpiece is 50 mm (step 122). If the operatoraccepts the information displayed by the display 2 (step 123), a thermalspraying operation can be carried out under spray conditions includingvalues tabulated in Table 6.

TABLE 6 Spray Condition For Frustum Values For Inlet Values for SprayParameters and Outlet Region Middle Region Spray distance (mm) 50 80Moving velocity (mm/s) 500 150 Spraying angle (deg) 90 80 Current (A)600 600 Voltage (V) 60 60 Plasma gas: Ar (l/min) 40 40 Auxiliary gas: H₂(l/min) 7 7

Although the present invention has been described in its preferredembodiment and examples, the present invention is not limited thereto inits practical application and various changes and modifications may bemade therein without departing from the scope and spirit thereof as setforth in appended claims.

What is claimed is:
 1. A thermal spraying method using a thermalspraying apparatus provided with a thermal spraying gun, and a computerfor determining spray conditions, said thermal spraying methodcomprising the steps of: (a) entering shape data on the shape of aworkpiece into the computer; (b) determining a set of values of sprayparameters and a path of the spraying gun, the determining stepincluding the steps of: (i) selecting representative values of the sprayparameters from a spray condition database of the computer, which storesa plurality of values for each of the spray parameter; (ii) calculatinga path for the thermal spraying gun on the basis of the values of thespray parameters selected in the step (i) and the shape data on theworkpiece according to a program stored in the computer; (iii) decidingwhether or not thermal spraying can be carried out by moving the thermalspraying gun along the path calculated in the step (ii) according to theprogram stored in the computer; and (iv) repeating, if it is decidedthat thermal spraying can not be carried out in the step (iii), thesteps (i), (ii) and (iii) at least once, while changing at least one ofthe value of the parameters used in the previously executed step (i),the changed value of the parameter being selected from values stored inthe spray condition database; and (c) carrying out a thermal sprayingoperation on the basis of the values of the spray parameters and thepath for the thermal spraying gun determined in the step (b),  whereinthe set of values selected in step (i) at a beginning of the step (b)are optimum values specifying on optimum spray condition, under whichdense sprayed coating can be obtained, and wherein the set of valuesincluding the at least one value changed in the step (iv) specifies aspray condition under which a sprayed coating containing more or largervoids than those contained in the sprayed coating sprayed under theoptimum condition,  wherein the spray parameters include: spray distanced between the workpiece and the thermal spraying gun; angle θ betweenthe thermal spraying gun and the workpiece; and moving velocity v of thethermal spraying gun relative to the workpiece, wherein, at least one ofthe spray distance d, the angle θ and the moving velocity v is changedin the step (iv), and  wherein the determining step (b) including thesteps of: (v) displaying, on a display of the computer, a decision ofthe step (iii), and requesting from an operator which parameter amongstthe spray distance d, the angle θ and the moving velocity v should bemaintained or changed in the step (iv); and (vi) inputting, by theoperator into the computer, at least one parameter amongst the spraydistance d, the angle θ and the moving velocity v that should bemaintained or changed; wherein the steps (v) and (vi) are carried outafter the step (iii) and before the step (iv).